In the manufacture of cathode ray tubes, and in particular, color or polychromatic reception, it is necessary to utilize a sealing glass to adhere the frontal viewing portion of the CRT, known as the faceplate, to the rear portion of the CRT, known as the funnel assembly. The faceplate flange edge mates with a similar edge of the funnel and the two parts are sealed together by means of a sealing glass that has a melting point less than the melting point of the glass used in the fabrication of the faceplate and the funnel.
The sealing glass may be either vitreous or of a type that devitrifies after it has been thermally treated. The actual seal is effected by placing a prescribed layer or bead of sealing glass paste on the funnel edge adjacent the large end of the funnel. The sealing glass paste contains a predominate amount of finely ground particulate glass mixed with a vehicle to provide certain fluid characteristics to the mixture. The sealing glass paste, as it is known in the trade, must possess characteristics that permit its deposit on the glass edges that are to be sealed together to be quite even in overall cross-section and to remain in situ without undue distortion or flow until actual firing takes place. To create the most desirable sealing glass paste, not only must the glass particle size be carefully regulated, but also, the vehicle must be blended with thixotropic and gelling agents.
The actual mixing of the sealing glass is important and contributes greatly to a successful high speed assembly of CRT's utilized in the television industry. In the past, sealing glass in the powdered form was supplied to the CRT manufacturer. The powder was then combined with the proper amount of vehicle and the ingredients were then mixed in a standard industrial mixer of one type or another. The mixed sealing glass paste was then removed from the mixer after thorough agitation and then placed in a paste dispensing machine for direct application to the seal edge or edges of the glass parts to be joined together.
The actual preparation of the sealing glass paste by the CRT manufacturer as described above is an unwanted task, however, such in situ mixing of the sealing glass paste in the past was dictated because the paste had to be used shortly after mixing because of the inherent nature of the paste to increase in viscosity in an unpredictable manner, thus resulting in an unacceptable paste mixture. Then too, the CRT manufacturer was confronted with dust problems associated with the loading of the particulate sealing glass into the mixer.
During the formulation of a typical sealing glass suspension suitable for joining together glass components of a CRT, a pyrolyzable organic binder coupled with an organic solvent is utilized. A typical binder is nitrocellulose and a suitable solvent is amyl acetate. The range of the binder plus solvent is generally in the range of 6-10 percent by weight as it is combined with the heavier fritted glass powder.
Another problem encountered with paste suspensions was that they were susceptible to changes over a relatively short period of time. This change in paste characteristics directly affected the paste dispensing apparatus so that frequent adjustment of the dispensing apparatus was required in order to achieve a uniform bead or extrusion of the paste onto the edge or edges of the glass parts being readied for subsequent sealing together.
The undesirable characteristics of the prior in situ mixed sealing glass suspensions severely limited the useful life of the sealing glass paste plus caused an unwanted lead dust contamination in the workplace where the paste was mixed.
It is one of the main objects of the present invention to provide an improved sealing glass mixture with a consistant and predictable shelf life subsequent to the mixing thereof.
It is another object of the present invention to provide a technique for the confinement of all particulate contaminants during the mixing of the fritted glass and its binder solvent additive.
It is a further object of the instant invention to provide a sealing glass compatable with existing dispensing apparatus.